Articulated booms are well known in the art. See for example, U.S. Pat. Nos. 2,881,030; 2,940,539; 3,082,842 and 3,834,488. In operation, the upper arm is pivoted relative to the lower, which is itself pivotable, both to the desired positions. To maximize use capabilities, it is preferable that the boom have the capabilities of moving the arms through a vertically aligned co-linear position (centered position) to a vertically over-centered position. In an attempt to achieve maximum articulation, the prior art constructions provided individual hydraulic cylinders acting on the arms, pivoting on pins joining the arms, or employed cables or chains connected to the arms for relative movement of the arm. However, no articulated boom employing hydraulic cylinders and pin connection has provided relative rotation of the upper arm relative to the lower arm to exceed about 210.degree..
In an attempt to achieve a greater angular separation of the upper and lower arms the prior art articulated booms have employed chains or cables to rotate the upper arm relative to the lower arm. By employing chains or cables, angular separation of the two arms of about 270.degree. has been achieved. However, the strength of the cables or chains employed used to rotate and secure the arms is only as great as the weakest link of the chain or weakest part of the cable. Since these articulated booms are employed to lift workers on work platforms, for example, to repair hydro or telephone lines, safety is paramount to requiring 100% reliability and consequently, this approach has not been widely accepted in the industry.
Additionally, the use of cables and chains requires cumbersome supporting assemblies and widely restricts maneuverability of the articulated boom.
It is therefore an object of this invention to provide an articulated boom and assembly useful therewith which overcomes the aforementioned difficulties with the prior art, permitting safe relative angular rotation between the lower and upper arms of about 270.degree..
Further and other objects of the invention will be realized by those skilled in the art from the summary of the invention and detailed description of preferred embodiments thereof.